the hole in the axle will fit a 3/8" shaft almost all the way thru. I think I will have to drill the last couple of inches out by a 1/16" or so. the axle has a taper to it.

This could be exciting news! However, do you think it's safe to drill it out? I have not looked at the XR650R axle myself, I quickly looked at the XR650L axle and ruled it out. Would you be willing to post some pics of your axle and the Outside and Inside dimensions, and the overall length? Best if you could remove it for the measuring and pics... If not, no worries, I'll get ahold of one soon.